In a multistage cylinder a plurality of cylinders, and pistons, are arranged in a telescopic manner one within the other. Piston rings seal between each of the cylinders, and internal ports permit oil to flow for either extending or retracting the cylinders one within each other.
The free end of the outer or largest cylinder is adapted to be connected for performing work, and the free end of the smallest innermost cylinder is also adapted to be connected for doing work.
Oil may be supplied either through the largest cylinder, or along the axis of the smallest cylinder. Hydraulic fluid will thus cause all of the cylinders to be extended one from the other during a work stroke.
An inherent disadvantage of such multistage cylinders is the fact that the maximum force that can be exerted at a given pressure is controlled by the area of the piston on the smallest cylinder. It is of course well understood that the force exerted by any cylinder is determined by the pressure of the fluid, and the area of the piston.
Since in this type of cylinder all pistons work simultaneously, the maximum force that is available, is a product of the diameter of the smallest piston. It is, of course, well known that the volume of hydraulic fluid required to extend such of multistage cylinders is the product of the volumes of all of the cylinders. Consequently, very large volumes of fluid are required to fully extend multistage cylinders, and relatively high fluid pressures are required so as to obtain adequate force, for the purpose intended, from the relatively small piston area.
As a result, such multistage cylinders are relatively inefficient in terms of power consumption.
In many applications such as, for example, packing of refuse in a refuse container, where for example the cylinder may not always be used at full extension, the operation of all stages of the cylinder simultaneously for packing refuse will require very substantial fluid flows into and out of the cylinder for each packing and retraction cycle, where only a modest force is required. Full force will not be required until the cylinder is used to actually compact or wedge the refuse into a smaller space. Clearly, it would also be desirable to reduce the volume of fluid required for operating the cylinder during this stage of operation.
Secondly, it would be desirable if the largest diameter cylinder and piston could be operated independently so as to develop the full force available from the fluid over the entire area of the largest piston.